In this chapter from "CCNA BCRAN Exam Cram 2," the authors discuss CiscoSecure ACS, which is what provides a Cisco network with AAA capabilities. They also examine the three AAA servicesAuthentication, Authorization, and Accountingin detail.

The Cisco Security Options

Cisco provides IOS options and hardware products to help secure your network
and make securing the network easier. The router IOS now has a number of
security options, such as virtual private network (VPN) capabilities and
integration with intrusion detection system (IDS) sensors and the firewall
feature set.

Each of the different security options is also available as a separate
security appliance; typically, an appliance is another piece of hardware
designed for a specific task. Some of the different appliances follow:

VPN concentrators and hardware clientsAn appliance designed
specifically for encryption and decryption to offload the work from routers,
servers, workstations, and other infrastructure devices.

IDSsAvailable to examine traffic passing along the wire
looking for known signatures of attacks as well as other anomalies. One IDS
option is an add-on card for the 6500 catalyst switch, a separate appliance for
critical servers, known as a host-based IDS.